U.S. Pat. No. 3,471,924 to Iles relates to a method of forming a p.sup.+ n cell. A p.sup.+ skin is formed on an n-type or p-type bulk silicon base, and the skin is removed from one side of the base. The exposed bulk silicon is then subjected to vacuum deposition with lithium and heated to a temperature between 350.degree. and 550.degree. C. The lithium causes an n-type silicon base to become highly doped and have a low resistivity. The lithium also causes a p-type base to become very highly doped n-type.
U.S. Pat. No. 3,490,965 to Webb discloses a p-n junction formed by starting with an n-type base, forming a p region by passing boron nitrate vapor over the base at a high temperature, and introducing lithium into the n region by diffusion of a lithium paste applied to the surface of the n region. The wafer is then heated to about 400.degree. C. for about an hour to diffuse the lithium through the entire n region into the p region. The result is a solar cell which is radiation resistant.
U.S. Pat. No. 4,147,563 is concerned with the formation of a p-n junction. The patentee utilizes laser diffusion to accomplish the desired result.